Apparatus for vaporizing metal



m55 www Sept. i6, 1969 w. A. BOX ET AL. 3,467,058

APPARATUS FOR VAPORIZING METAL Filed Dec. 1965 I l l fr/I/ /f//l/ 111,1

INVENTORS. 4WILL/IMI A. BOX and IVI/11 2l A f farhey United States Patent 3,467,058 APPARATUS FOR VAPGRIZING METAL William A. Box, Fullerton, Calif., and Waldo Rall, Fox

Chapel, Pa., assignors to United States Steel Corporation, a corporation of Delaware Filed Dec. 3, 1965, Ser. No. 511,515 Int. Cl. C23c 13/12 U.S. Cl. 11S-49.5 1 Claim ABSTRACT OF THE DISCLOSURE f of the metal bath from which vapor evolution occurs,

thus avoiding spattering and splashing.

This invention relates to the vaporization of metal and, in particular, to a method and apparatus for vaporizing metal at a substantial rate, as for the purpose of coating a traveling strip by condensation in a vacuum.

Vacuum-deposition lines for coating strip traveling at even moderate speeds require the vaporization of coating metal from a crucible at a substantial rate. This immediately presents a problem of supplying make-up coating metal, through the wall of the vacuum chamber, to the crucible containing the molten coating metal from the surface of which evaporation takes plate. It has been proposed to feed metal in wire form from the outside of the chamber into the crucible. Regardless of the form in which make-up metal is supplied, the high rate of the melting thereof which is necessary, causes the gases super cially associated with the coating metal, e.g., aluminum, or dissolved therein, to erupt or evolve violently. Spattering and splashing of the molten metal in the crucible may result with objectionable effects such as marring the strip being coated or short-circuiting the electron-beam gun which is the means usually employed to heat the surface of the molten metal.

It is, accordingly, the object of our invention to provide a method and means for supplying make-up metal to a vaporization crucible, which isolate from the surface of the bath from which vaporization occurs all violent eruption or vigorous evolution of gas from the make-up metal as' it is melted. In a present preferred embodiment and practice of our invention, we provide, in addition to the crucible containing the molten metal heated to vaporization temperature, a fusion chamber or pool adjacent thereto and communicating therewith, but separated therefrom, both above and below the surface of the molten metal. We further provide means for introducing solid make-up metal into the fusion chamber and causing the flow thereof, when melted, into the main bath below the surface thereof.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the drawings:

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FIGURE 1 is a plan view of a crucible incorporating our invention with its related electron-beam gun;

FIGURE 2 is a longitudinal section through the crucible showing make-up metal-feeding means associated therewith; and

FIGURE 3 is a cross section taken along the plane of line III-III of FIGURE 1.

Referring now in detail to the drawings, a crucible 10 comprises a trough or boat 11 of refractory metal, an outer sheath 12 of metal and alternating layers 13 and 14 of molded and granular insulation therebetween. Such crucible is described and claimed in the copending application of Joseph K. Swindt, Ser. No. 439,238, led Mar. 12, 1965, now Patent No. 3,345,059. The crucible is adapted to contain a charge of metal 15 to be melted and vaporized. Heat may be generated at the exposed surface of the charge in the known manner by the impact thereon of electrons from a gun 16. The path of the electrons is made curvilinear by a magnetic eld in the direction of the length of the crucible.

A wall 17 of refractory material such as alumina, standing on the upper edge of the crucible 10 includes an end portion 18, a side portion 19 and a portion 20 disposed transversely of trough 11. Portion 20 depends into the trough but terminates short of the bottom thereof, leaving a passage 21 connecting an end portion 22 of metal bath in the trough with the remainder thereof, designated 23. This main portion 23 of the metal bath is the target of electrons from gun 16, the paths being generally indicated at 24, and vaporization of the metal constituting charge 15 takes place from the surface of portion 23. Portion 22 constitutes a fusion pool for supplying make-up metal to portion 23. The strip to be coated is passed over portion 23 as indicated at 25 in a direction normal to the length of the crucible.

Make-up metal is introduced into fusion pool 22 by any suitable means such as pinch rolls 26 for feeding metal in wire form. The pinch rolls may be located inside or outside the vacuum chamber enclosing the crucible and the portion of the strip undergoing coating. Tubular guides (not shown) may also be needed to direct the wire accurately into pool 22. Metal wire fed into pool 22 s melted by heat absorbed from bath portion 23 through the walls of trough 11. It will be understood that the supply of make-up metal is closely correlated with the loss of metal by vaporization and that the level of liquid metal in the two bath portions 22 and 23 is equalized by flow through passage 21.

By maintaining a fusion pool separate from the remainder of the molten bath where vaporization occurs, and feeding make-up metal into the fusion pool only, we avoid the disturbance of the main portion by the evolu tion of gas from the make-up metal on melting thereof. We thus eliminate spattering and splashing of molten metal from the main portion onto the strip being coated and onto the adjacent apparatus in the vacuum chamber. Wall 20 also tends to prevent stray electrons from gun 16 from reaching the fusion pool 22. Since feed wire is melted in pool 22 by heat absorbed from bath portion 23, the former is at a lower temperature than the latter, thereby reducing the possibility of substantial vaporization from the surface of pool. 22n

We claim:

1. In a vacuum-condensation apparatus for coating sheet material, means to support the material, an elon-x gated crucible extending horizontally below the material for holding a bath of molten coating metal, a cross wall in said Crucible adjacent one end thereof defining adjoining but separate fusion and vaporization chambers, said vaporization chamber being disposed below the material and said fusion chamber laterally, thereof, said wall having a passage below the surface of the bath connecting said chambers to establish a common liquid level therein, and extending to a substantial height above said surface to form a partition between said chambers, electron-beam means adjacent the Crucible for topfheating the surface of the bath in the vaporization chamber only, and means feeding solid metal into said fusion chamber,

References Cited UNITED STATES PATENTS ALFRED L. LEAVITT, Primary Examiner 10 A. GOLIAN, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent No. 3,467,058 September 16, 1969 William A. BOX et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, J r.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

